Method of casting foam insulation for an elongated member



E. ANDERSEN July 23, 1968 METHOD OF CASTING FOAM INSULATION FOR ANELONGATED MEMBER Filed June 15, 1964 INVENTOR. Es E A N o E RSE N BYATTORNEY United States Patent 3,394,207 METHOD OF CASTING FOAMINSULATION FOR AN ELONGATED MEMBER Ege Andersen, Logstor, Denmark FiledJune 15, 1964, Ser. No. 375,274 8 (Ilaims. (Cl. 264-45) ABSTRACT OF THEDISCLOSURE A method of forming a thermally-insulated pipe by casting aninsulating foam substance about pipe sections prior to lowering saidsections to a horizontal position in which they become part of anunderground pipeline. Each pipe section is inserted into a tubularcasing section of appreciably larger diameter and maintained insubstantially upright position, with the shield resting upon a surfaceand closed off thereby at its bottom. At least one of said sections iscoated with a lubricant, and a charge of foaming plastic is introducedinto the space between the pipe section and the casing section andallowed to rise and set to completely fill said space with foaminsulation. The pipe section, casing section and foam insulation arethen lowered as an integral unit to a horizontal position, with thelubricant serving as a slipping agent to allow for thermal expansion orcontraction of the unit parts.

This invention relates to a novel and improved method for casting athermal insulating foam substance between an elongated body such as ametal pipe and an outer protective shield such as a plastic tube. Theinvention is particularly applied to the insulation of heating andcooling pipes which are laid underground beneath the street.

It is known to insulate district heating pipes, for example, by layingthem in street excavations within a jacket consisting of the upper andlower sections of a split concrete shell, and then pouring porous orcellular concrete into the space between the district heating pipe andthe concrete shells.

Since such casting is performed after the pipes are laid in the street,the pipes and the concrete jackets necessarily are substantiallyhorizontal at the time of casting. In order to avoid such inherentdisadvantages as the formation of cavities due to improper fillingbetween the district heating pipe and the outer shell, the cellularconcrete must be poured through inlets at mimimum intervals, forexample, six feet or less, which makes the operation extremelytime-consuming.

In the aforementioned conventional method of casting insulation, thecellular concrete becomes firmly coherent with the surrounding concreteshell, and if the cellular concrete also becomes coherent with the innerheating pipe it tends to become crushed due to the thermal expansion orcontraction of the heating pipe. In order to avoid this crushing, theheating pipe is wrapped in corrugated paper, thus establishing in thehigh temperature region, an uninsulated longitudinally-extending heattransmission path, which causes, in combination with unavoidable radialcracks and other unavoidable insulation defects in the cellularconcrete, appreciable heat losses to the surrounding soil.

In the German patent application DAS No. 1,016,992, there is taught amethod of casting an insulating foam substance around heating pipes atthe time of. laying the latter. In this method, a wide mesh hose is usedas a mould, the hose being stretched out around the heating pipe byspacing means. This hose, being woven of jute, fibre glass or wire,offered no protection against impact, and therefore, it was oftennecessary to resort to the cumbersome procedure of covering the hosewith a jacket of concrete, tin plate, asphalt, impregnated paper etc.,which, of course, further increased the costs of the already expensivemethod of casting on site.

In addition, it has recently been suggested to insulate cooling pipes bycasting around them a polyurethane foam substance enclosed in a jacketof galvanized sheet metal formed in the usual manner employed for makingsuch metal sheaths. This again is an instance of casting at the site oflaying the pipe, with all of its attendant disadvantages. Further, itproved disadvantageous to use a protective jacket of sheet metal, which,in the course of time, would rust away and then he incapable ofprotecting the shock-vulnerable foam insulation.

Where polyurethane was used as a. foam substance, it has been found thatexcellent adhesion to the cooling pipe was attained, which is consideredan advantage insofar as the insulating of cooling pipes is concerned. Onthe other hand, where heating pipes are to be insulated, a free mobilityof longitudinal movement between the heating pipe and the insulatingmaterial, and between the insulating material and the surroundingprotective jacket or casing must be sought for in order to avoidtransverse cracks in the insulating layer.

In cooling applications, there is particular interest in providing afirm and unbroken connection between the cooling pipe and the waterproofinsulating medium, since otherwise sweating or condensation willinevitably destroy the thermal insulating capacity of the insulatingmaterial, possibly throw off the material, and in the course of the timecause the pipe to rust. However, since foam insulation material tends toadhere even more firmly to the outer jacket or casing, adverse radialexpansion cracks very soon develop in the insulation.

An object of the present invention, is to provide a method of casting athermal insulating foam substance between a pipe to be insulated and anouter sheath, preferably a plastic tube, which method avoids theaforementioned difiiculties inherent in conventional methods.

It is another object of the invention to provide a process for theindustrial casting in quantity of tight and durable insulation aroundelongated bodies such as pipes of uniform length, in such a manner as toavoid the tendency for the development of insulating defects incurredeither during the casting operation, or following extensive use, or byreason of large fluctuations in temperature.

The method of casting foam insulation in accordance with the presentinvention, is characterized in that the casting is performad with theelongated pipe and easing disposed in a rather steep position,preferably vertically upright. The pipe, which is preferably metal, isdisposed within the casing and spaced from the walls thereof. The bottomend of the casing is closed off either by a metal plate, or by a plugformed by pouring a small amount of foaming insulation material into thetube and allowing it to set at the bottom thereof. Into the spacebetween the inner pipe and outer tube there is then poured a measuredamount of plastic containing a foaming agent and setting agent, and theplastic is allowed to foam and rise until it completely fills the tubeand hardens to provide a filler of foam insulation between the tube andthe pipe.

A lubricating coating is applied to the outer surface of the inner pipeand/or to the inner surface of the outer tube to provide longitudinalslippage between these parts and the cast foam insulation. If the pipeis used for cooling or refrigeration, the lubricating coating is appliedonly to the outer tube. The casting may be performed in a fractory orother site remote from the street excavation into which the insulatedpipe is subsequently to be laid.

Another object of the invention is to provide a casting method of thecharacter described which may be performed by industrial or workshoptechniques, eliminating the formation of cavities even though pipes andcasings of considerable lengths are cast in a single operation. Thisnovel process also avoids the formation of radial cracks in theinsulating material during the casting operation, since the body weightof the insulating material in the vertically-disposed casing willproduce a slight compressive stress during the setting or hardening ofthe insulation.

Additional objects and advantages of the invention will become apparentduring the course of the following specification when taken inconnection with the accompanying drawing which is a vertical sectionalview showing the manner in which polyurethane foam insulation is castbetween a metal pipe and its outer sheath or casing.

Referring ni detail to the drawing, the numeral designates a pipe suchas a district heating pipe of the usual type, which is conventionallymade of metal such as steel. Surrounding the pipe 10 is a jacket orcasing in the form of a tube 12 preferably made of polyvinyl chloride(PVC), and of substantially the same length as the pipe 10. The pipe 10is of substantially smaller diameter than the outer tube 12, and isconcentric therewith. Both the pipe 10 and tube 12 are shown in avertical position which is preferable for the casting operation,although it is not essential in that the members be vertically disposed.Any upright angle sufficiently steep to enable the foam material pouredtherein to fill the outer tube 12 by action of gravity, would suffice.The outer tube 12 rests and is covered over at its bottom end by a baseplate 14.

With the tube or casing 12 disposed in upstanding position and the pipe10 centered therein and spaced from the walls thereof, the insulation iscast about pipe 10 by pouring into the space between the pipe and thecasing, a foam plastic mixture consisting of a plastic such aspolyurethane, a foaming agent or propellant therefore, and a settingagent, so that the plastic charge foams and rises within the tube.

To eliminate the necessity for cumbersome trimming and pluggingoperations before the casting of the insulation, which operationsrequire the purchase and use of expensive precision tools, the castingprocess described herein makes it possible to first cast a short lengthof the insulation material to serve as a tight bottom plug. The drawingshows such a bottom plug 16 which is formed by pouring a small amount offoam plastic casting mixture into the top of casing 12 and allowing themixture to foam and set providing a seal at the bottom of casing 12.Thereafter, the main charge of plastic foaming mixture is poured intothe casing, and the foam insulation is cast in lengths (heights) aslarge as possible without forfeiting uniform specific density of thefoam material along the entire extent of the casting. Careful pluggingat the bottom of the pipe assembly is desirable for economy where longpipe lengths are to be packed in a single operation, although where thecasing end surface rests snugly upon the plate, the latter may serve asa seal and the formation of the bottom plug may be omitted.

After the plug 16 has hardened so that it adheres to both the outersurface of pipe 10 and the inner surfaceof casing 12, and thus seals offthe bottom of the latter, the polyurethane casting mixture is pouredinto the space between the pipe and tube and allowed to rise until theentire tube is filled with foam insulation. After the insula- .4 tion iscompletely set, the unit is brought to a horizontal position and isready for use.

An important feature of the invention is that the process is capable ofbeing performed at a factory or other location remote from theexcavation site. The pipe with its foam insulation and outer casing issubsequently brought as a unit to the excavation site where it is laidinto the excavation. The process of the invention thus not only enableslong pipe sections to be insulated in a single operation, but it avoidsthe current difficulties of applying insulation of the pipes at theexcavation site and after they have been laid'in horizontal position.

The casting mixture employed for the formation of both the plug and themain foam insulation comprises a flowable plastic such as polyurethanemixed with a propellant and foaming agent therefore as well as a settingagent. The foaming and setting agents are well known and commerciallyavailable.

In order to avoid undesirable longitudinal stresses in the foaminsulation (radial stresses being of minorsignificance), a slippingagent or lubricant should be applied to the outer wall of the pipe 10and/or the inner wall of the casing 12. This slipping agent may beintroduced either before or during the casting of the foam insulation toprevent the latter from sticking to the casing 12 and/or to the pipe 10.Of course, where a cast plug 14 is provided, the slipping agent isomitted from the bottom portion of the pipe and easing at which thebottom plug is to be formed.

By the use of such slipping agent or lubricant, the cast foam insulatingmaterial is prevented from following the longitudinal expansion andcontraction of the pipe and its casing at varying temperatures, andaccordingly the formation of cracks in the insulation due to suchmovement, is eliminated. Since the slipping agent is applied in the formof a very thin film adhering to the pipe or casing, no harmful air gapwill result between the pipe and the insulation, and no loss of heatwill be caused by such a gap.

Where insulating material is cast about cooling pipes by the process ofthe present invention, it is desirable that the insulating materialadhere firmly to the cooling pipe, and therefore the slipping agent orlubricant is applied only to the inner surface of the outer casing. Forthe insualtion of refrigeration pipes, for example, it may in certaininstances prove labor saving if the slipping agent or lubricant isselected from the type which will adhere or dress better to the plasticmaterial of the outer casing than to the metal surface of the pipe. Inthis way, time-consuming care need not be devoted to preventing tracesof the lubricant from coating the inner pipe which is to be insulatedagainst loss of cold. Where the pipe is made of plastic, such selectedlubricants can be easily determined and are readily avail ablecommercially. For example, if, according to the method herein, thelubricant is applied at the time of casting the foam insulation, alubricant containing a substance which acts as a plasticizer for theplastic material of the casing will be found to adhere much more readilyto the inner wall of the casing than to the outer wall of the metalpipe, and consequently will coat the former rather than the latter.Where the casing is madein its preferred form from PVC polyvinylchloride, any of the well-known plasticizers for the same may beemployed as the slipping agent. Plasticizers for other plastics will beevident in the literature, and are well-known to those skilled in theart.

In addition, to its function in providing selective application of alubricant, the use of molded plastic as the constituent material for theouter casing effects a number of other advantages. These include hightensile strength, corrosion resistance, contribution to. thermalinsulation, minimum weight and bulk, electrical insulation as protectionagainst stray currents, etc. 7 1

ln accordance with the invention, the process contemplates the preferreduse of a lubricant or slipping agent containing stearates, for example,a mixture of calcium and magnesium stearates mixed with oil and alcohol.

The oil may be of any of the standard inert oils which will evaporate soslowly that vapor bubbles or steam pockets are avoided. The oil actspartly as a lubricating medium, but also, and perhaps principally, as asuspension and distributing agent for the stearates which will cause thelatter to form a film upon the wall of the outer casing. The alcohol maybe any volatile type which provides an effective mixing by stirring ofthe stearates in the oil. The alcohol is volatile so that it willevaporate completely before the casting around the pipe is commenced,eliminating risk of formation of air pockets dur ing casting.

The use of paste-like lubricants in the instant process is undesirableand should be avoided, since the precise application of such lubricantsin a fine uniform film on the inner surface of the casing would involveconsiderable manual work. In addition, such a film of paste would beeasily damaged when the inner pipe is inserted. into the casing, andcontact would cause unintentional coating of the inner pipe, which, aspreviously indicated, is disadvantageous in the case of cooling pipes.To facilitate the process, therefore, it is possible to use a lubricantor slipping agent, in powder form, which powder is poured on top of therising foam plastic and kept in a state of agitation within the outercasing by swirling or vibrating the same directly above the surface ofthe rising foam material. The powder may be a mixture of calcium andmagnesium stearates, as previously described. A reliable manner ofspreading a thin lubricant film of such powder on the inner wall of thecasing and outer wall of the pipe, is by maintaining the lubricatingpowder in continuous motion by agitating means, for example, by an airjet emitted by a nozzle held slightly above the rising level of thefoaming plastic. The pressure of the air jet need only be sufficient toswirl the powder about above the level of the rising foam, so that, asthe foam rises, the powder forms a uniform thin coating on the walls ofthe pipe and casing.

The lubricating powder is added immediately after the plastic foammixture is poured into the casing and before it begins to riseappreciably, by pouring a quantity of the powder onto the top surface ofthe plastic charge. The powder does not mix with the rapidly-expandingviscous foam, but if it were not agitated as described, there would be atendency for the pile of powder to be entrapped in irregular thicknessesbetween the rising foam materials and the walls of the pipe and casing.Such enclosed amounts of powder would be lost as a lubricant and wouldcause irregular defects in the insulating material.

The lubricating of the casing and/or pipe walls will, as previouslyindicated, serve to avoid longitudinal stressing of the insulatingmaterial as the pipe or casing expands or contracts under temperaturevariations. The lubrication is further advantageous in avoidingundesirable residual stresses in the insulating material incurred duringthe casting operation.

For a better understanding of the process contemplated by the presentinvention, reference is now made to the following examples constitutingspecific illustrations of the process as employed for heating andcooling pipes.

Example I.Thermal insulating of a district heating line The steelheating pipes employed are commercially supplied pressure tested and inlengths of twenty feet. The tubular casings for these pipes are made inlengths of nineteen feet and four inches and are in the form of moldedpolyvinyl chloride pipes without pipe sockets.

Each steel pipe may be first lubricated on its exterior surface using anoil-stearate mixture, as previously described, and is inserted within acasing 12. Both the casing and contained pipe are hoisted to a verticalposition and supported in such a manner that the steel pipe 10 iscentered within the casing 12, as shown in the drawing with the steelpipe projecting from both ends of the casing by approximately fourinches. The bottom end of the casing 12 rests upon the sealing baseplate 14, which, where only minor static head. pressures are involved,can itself create a sufficient seal to prevent the plastic insulationmaterial from leaking out of the bottom of casing 12.

The organic foam casting mixture is now poured into the space betweenthe pipes. The mixture consists of polyurethane to which the foamingagent. and setting agent have been added immediately before pouring. Thequantity of the mixture initially poured out has been exactlyproportioned by weighing or measuring so that it will expand and hardento form a base plug 16 of suflicient height to provide an effectiveseal, but low enough to render negligable the static or head pressure atthe 'bottom of the casing 12, and also low enough so that frictionagainst the walls of the pipe and casing will not be sufficient to causeappreciable downward foaming pressure.

As previously indicated, if the base plate and the bottom end of casing12 are finished with such precision as to make a snug fit, thesurface-to-surface contact therebetween provides a sufficient seal andthe step of preliminarily forming the plug may be omitted.

After a short time, approximately one minute, the plug becomeswell-hardened, and a measured charge of casting mixture is poured downinto the space between the pipe 10 and casing 12. This measured mixtureof polyurethane and its propellant and setting agents, has beencarefully weighed and is in the amount determined by experience tocompletely fill up the space between the pipe and easing at theprevailing temperature.

The drawing shows a charge of polyurethane mixture 18 after it has beenpoured and as it is starting to foam and rise within the casing 12.

Where the pipe is not initially lubricated, an apportioned quantity ofpowdered lubricant (calcium and magnesium stearate) is poured down onthe top surface of the foam mixture, and a pneumatic hose with a nozzleis lowered into the space between the pipe and casing to a point justabove the powder. As the foam insulation rises within casing 12, thepneumatic hose is continually lifted so that the nozzle is always justabove the surface of the foam, and the air flow is increased ordecreased as desired. The swirling powder thus coats the surfaces of thepipe and easing just above the rising foam.

After the polyurethane foam has filled the casing 12 and has set, andonly after setting, the casing and enclosed pipe are lowered to ahorizontal position. Subsequently, a sharp knife is used to clean bothends of the casing of excess foam projecting from the casing, by radialcuts toward the center heating pipe.

The assembled insulated heating pipe is then brought to the site of thestreet excavation. A rubber ring is placed around each end of the casing12 and a wide PVC collar, of a diameter to pass freely over the rubberring, is slid onto one end of the casing. This PVC collar is made as ashrink collar, that is, it has in a heated state been stretched from anormally smaller diameter, and upon reheating will shrink toward itsoriginal size. One of the projecting four-inch lengths of the steel pipe10 is now joined by welding to the projecting length of steel pipe ofthe preceding unit. When a sufficient length of conduit or pipeline hasbeen welded together, the welded joints are pressure-tested.

Two eight inch half sections of polyurethane foam tubular shells areplaced tightly around the steel pipe, and glued securely thereto. Anygood synthetic resin glue of the abundant commercial types, which willadhere to polyurethane foam and to metal (without dissolving thepolyurethane), may be used, or foaming polyurethane may be employed asthe glue. The PVC collar is then pushed over the covered joint. untilthe collar is centered upon and covers the joint section, and the collaris reheated until it shrinks around the two rubber 7' rings, providing atight seal and protection against damage.

The narrow ditch or trench surrounding the PVC casings may already befilled in before the welded pipe joints are pressure-tested, avoidingconsiderable nuisance in the street excavating operation. However, theditch at the region of the welded pipe ends is not filled in with earthuntil the collars have been placed in proper position and secured byshrinking.

Shut-off valves and similar irregular fittings in the pipeline can beinsulated by means of shrink collars in the same manner as described inconnection with the pipe joints, these fittings being previously encasedin cast polyurethane shells glued or otherwise secured around them, andhaving cylindrical outer surfaces. The shrink collars, for this purpose,must normally be slightly wider than the collars for the pipe joints, inorder to provide for uniform thickness of insulation. Further, thesecollars may be provided with a radial aperture for passage of the valvestem, which, if desired, may be sealed watertight, for instance, bymeans of a synthetic rubber gasket.

Example 2.Insulating of cooling pipes The procedure is substantially thesame as described above under Example 1, except that special care mustbe taken to insure that an unbroken and close-fitting insulation isprovided around all pipes, fittings, valves and the like, and that thelubricant is applied only to the inner wall of the PVC casing, aspreviously explained.

In this instance, the lubricant is preferably a PVC plasticizer whichwill form a coating upon the inner surface 'of the PVC casing morereadily than upon the metal pipe. This is applied to the interior of thecasing before the foam insulation rises therein, and results inproviding the necessary slippage between the insulation and the outercasing but not between the insulation and the inner metal pipe.

It may then be appropriate, in order to avoid even narrow paths of coldconductivity, when gluing the foam polyurethane shells onto the exposedwelded pipe sections, as previously described, to use foamingpolyurethane as the gluing agent. Immediately after the placement ofthese shells, which are first dipped in or coated with foamingpolyurethane, the shells are carefully assembled, aligned and clampedtogether in order to preserve their correct assembled position after thesetting and hardening of the polyurethane foam, which adheres to boththe shell and the inner pipe.

In order to prevent considerable loss of the foaming polyurethane usedas the gluing agent, the work should be so arranged that a number ofgluing operations can be performed uninterruptedly in immediate sequencebefore the foam has time to set. Thus, a number of exposed welded pipesections are made available for insulating, and the foaming polyurethaneis stored in a vessel cooled sutficiently to reduce the foaming speed toa considerable extent. As soon as the cooled polyurethane mixture isapplied to the shells nad the metallic pipe surfaces at ambienttemperature, a normal foaming speed will again be restored.

What I claim is:

11. A method of forming, as an integral unit, a thermally insulated pipeto be laid in a horizontal position, comprising the steps of (a)enclosing an industrial length of pipe section in a hollow tubularcasing section of substantially the same length as said pipe section andof appreciably larger diameter,

(b) placing said casing section and enclosed pipe section in asubstantially upright position with the enclosed pipe section spacedfrom the interior surfaces of the casing section to provide an annularspace therebetween,

(c) closing off the bottom end of said casing section,

(d) coating the surface of at least one of said sections with a thinfilm of lubricant,

(e) pouring into the space between the upright pipe and casing sectionsa charge of plastic foam comprising a mixture of plastic, and foamingand setting agents therefor, such that the composition will settle atthe closed lower end of the casing section and foam and rise therein,

(f) allowing the composition to foam and rise until it fills the uprightcasing section and sets therein to provide permanent continuous foaminsulation between the pipe and casing sections along the entire lengthof said casing section with the set foam insulation joining said pipesection to said casing section to provide said integral unit, and withsaid lubricant serving as a slipping agent providing limitedlongitudinal slippage between the set foam insulation and the coatedsurface to allow for expansion or contrac tion of the unit parts, and

(g) thereafter lowering the integral unit to a horizontal position forlaying the same.

2. A method according to claim 1 in which the lubricant is applied onlyto the inner surface of the casing 'section and the foam insulation ispermitted to adhere to the outer surface of said pipe section.

3. A method according to claim 1 in which said pipe section is made ofmetal and said casing section is made of plastic, and in whichsaidlubricant is of a typewhich will form a coating more readily upon thesurface of the plastic casing section than upon said pipe section.

4. A method according to claim 3 in which said lubricant contains aplasticizer for the plastic material constituting said casing section.

5. A method according to claim 1 in which the lubricant contains amixture of calcium and magnesium stearates in a carrier of oil andalcohol.

6. A method according to claim 1 which includes the steps of pouring aquantity of powdered lubricant onto the upper surface of said plasticfoam composition immediately after said composition has been inserted atthe lower end of said casing section and before said composition hasbegun to rise, and maintaining said powdered lubricant in a state ofagitation as the lubricant is carried upward along the casing by theupper surface of the rising foam insulation.

7. A method according to claim 6 in which said powdered lubricant ismaintained in a state of agitation by directing a stream of air thereonfrom a nozzle kept a slight distance above the surface of the risingfoam insulation.

8. A method according to claim 1 which includes the steps of initiallypouring into the space between the upright pipe and casing sections arelatively small amount of foam plastic composition, allowing thecomposition to foam and set to form a short plug of foam insulation atthe bottom of the casing section such that the plug adheres to both thepipe section and casing section, thereafter placing said lubricant on asurface of one of said sections which faces the other section, andthereafter pouring onto the upper surface of said plug a charge ofplastic foam composition sufiicient, upon rising, to fill the maximumextent of the upright casing section with foam insulation ofsubstantially uniform density.

References Cited UNITED STATES PATENTS 536,184 3/1895 Case 26438 XR1,003,730 9/1911 Freund 264338 XR 1,462,563 7/1923 Ohio 264-3381,518,254 12/1924 Copeman 264338 XR 2,015,207 9/1935 Weller 264-3382,081,867 5/1937 Gysling 26445 XR 2,865,868 12/1958 McKinley et a1.

(Other references on following page) UNITED STATES PATENTS OTHERREFERENCES 5/1960 Tillman 106*38-24 Wood, R. N.: IBM TechnicalDisclosure Bulletin, vol. 12/ 1960 Heroy et a1 264-54 XR 3, No. 10,March 1961, Foamecl Air Bearing Cylinder." 11/1961 Ammons 264-54 XRRubber and Plastics Age article, Formed Core Panels 11/ 1961 Urban 264545 for Transport, vol. 44, N0. 5, pp. 499-500.

5/ 1962 HOlShOller 1 4 X Hoppe, Peter: Sandwich Laminates by In-Situ PU1/1966 Helfner 26445 X Foaming. In Plastics, January 1965', pp. 71-77.

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